As an example of a slider crank mechanism, an engine's crankshaft converts reciprocating linear movement of a piston into rotational movement about a longitudinal axis to provide torque to propel a vehicle, such as but not limited to a train, a boat, a plane, or an automobile. Crankshafts are a vital part of an engine, and are a starting point of engine design. Crankshaft design affects the overall packaging of the engine, and thereby the total mass of the engine. Accordingly, minimizing the size and/or mass of the crankshaft reduces the size and mass of the engine, which has a compounding effect on the overall size, mass and fuel economy of the vehicle.
The crankshaft includes at least one crankpin that is offset from the longitudinal axis, to which a reciprocating piston is attached via a connecting rod. Force applied from the piston to the crankshaft through the offset connection therebetween generates torque in the crankshaft, which rotates the crankshaft about the longitudinal axis. The crankshaft further includes at least one main bearing journal disposed concentrically about the longitudinal axis. The crankshaft is secured to an engine block at the main bearing journals. A bearing is disposed about the main bearing journal, between the crankshaft and the engine block.
In order to reduce weight of the crankshaft, a hollow section may be formed into and extend through each of the crankpins and main bearing journals. The crankshaft is frequently formed or manufactured by a casting process, such as but not limited to a green sand casting process or a shell mold casting process. Any hollow sections formed into the crankpins and/or the main bearing journals are defined by a plurality of different cores that are placed within the mold during the casting process. Each of these different cores must be precisely positioned relative to each other and the mold to properly form the hollow sections in the appropriate locations.